IPA: /ˈwɪl.fəli/
KK: /ˈwɪl.fəl.i/
In a way that is intentional and done on purpose, often despite the consequences or rules.
She willfully ignored the warning signs and continued with her plan.
Willfully → It is formed from "will" (from Old English "willan", meaning to wish or desire) and "-fully" (meaning in a manner full of). The word "willfully" means in a manner full of will or intention, often implying a deliberate choice.
Think of someone acting with strong 'desire' ('will') and doing so 'fully' ('-fully') — that's why willfully means doing something intentionally.